Facilitating communication and power transfer between electrically-isolated powered device subsystems

ABSTRACT

A system employing power over Ethernet (PoE) technology may include at least one powered device and power sourcing equipment (PSE). The powered device may include a first powered device (PD) subsystem and a second powered device (PD) subsystem that is electrically isolated from the first PD subsystem. The powered device may also include an interface connecting the first PD subsystem and the second PD subsystem. The PSE may be operable to provide power to one or more of the PD subsystems through a link connecting the PSE to the powered device. Also, the first PD subsystem may be operable to receive a communication from and transfer power to the second PD subsystem through the interface while maintaining the electrical isolation.

TECHNICAL FIELD

The present disclosure relates generally to power over Ethernet (PoE)technology.

BACKGROUND

In power over Ethernet (PoE) technology, power sourcing equipment (PSE)may provide power over a standard twisted-pair Ethernet cable to one ormore powered devices (PD) in an Ethernet network. This technology may beuseful for powering network devices when it is undesirable to supplypower through a separate connection. For example, an IP telephone may beconnected to an Ethernet cable that transmits data and provides powerwithout requiring a second wire to provide power via an electricaloutlet, for example. The IEEE 802.3 standard specifies requirements forPoE devices. Over time, the complexity of PDs has increased. With thisincrease in complexity, the power required by these PDs has alsoincreased.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is made to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 illustrates a system for facilitating communication and powertransfer between electrically-isolated powered device (PD) subsystems;

FIG. 2 illustrates a network device that facilitates communicationbetween electrically-isolated PD subsystems;

FIG. 3 illustrates example interfaces that maintain electrical isolationwhile allowing communications to be sent through the interface;

FIG. 4 is an example circuit for reporting that a PD subsystem isunderpowered;

FIGS. 5A-5B illustrate example circuits for transferring power betweenelectrically-isolated PD subsystems; and

FIG. 6 is a flowchart illustrating a method for obtaining power andreporting an under powered condition utilizing communication and powertransfer between electrically-isolated PD subsystems.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

In particular embodiments, a system comprises a powered device and powersourcing equipment (PSE). The powered device comprises a first powereddevice (PD) subsystem, a second powered device (PD) subsystemelectrically isolated from the first PD subsystem, and an interfaceconnecting the first PD subsystem and the second PD subsystem. The powersourcing equipment (PSE) is connected to the powered device by a linkand is operable to provide power to the first PD subsystem through thelink. The first PD subsystem is operable to receive a communication fromthe second PD subsystem through the interface and to transfer power tothe second PD subsystem through the interface.

In certain embodiments, a method comprises receiving a first amount ofpower at a first PD subsystem from a PSE and receiving an identificationof a second amount of power from a second PD subsystem. The secondamount of power represents a power deficit of the second PD subsystem,and the second PD subsystem is electrically isolated from the first PDsubsystem. The method further comprises, based on the first amount ofpower and the second amount of power, determining whether to transferpower from the first PD subsystem to the second PD subsystem andmaintaining electrical isolation between the first PD subsystem and thesecond PD subsystem when power is transferred from the first PDsubsystem to the second PD subsystem.

Description

FIG. 1 illustrates a system, indicated generally at 10, for facilitatingcommunication and power transfer between electrically-isolated powereddevice (PD) subsystems. As illustrated, system 10 includes a network 12,power sourcing equipment (PSE) 14, and a powered device 16, whichincludes two PD subsystems 18 and an interface 20. A link 22 connectspower sourcing equipment 14 to powered device 16 and its PD subsystems18.

Network 12 connects the elements in system 10 to other devices (notillustrated) and/or networks (not illustrated). In particularembodiments, network 12 is part of an Ethernet network. Network 12 maycontain any suitable communication equipment, including hardware and anyappropriate controlling logic. Network 12 may include a local areanetwork (LAN), metropolitan area network (MAN), a wide area network(WAN), any other public or private network, a local, regional, or globalcommunication network, an enterprise intranet, other suitable wirelineor wireless communication link, or any combination of any suitablenetwork(s). Network 12 may include any combination of gateways, routers,hubs, switches, access points, base stations, and any other hardware orsoftware implementing suitable protocols and communications.

Power sourcing equipment 14 provides power to powered device 16 and itsPD subsystems 18. Power sourcing equipment may be abbreviated PSE. Asillustrated, power sourcing equipment 14 provides power to powereddevice 16, PD subsystem 18 a, and PD subsystem 18 b; however, it isunderstood that any configuration of components may be employed. Forexample, multiple PSEs can be employed to provide power to powereddevice 16 and/or PD subsystems 18. Power sourcing equipment 14 may be anendpoint PSE or a midspan PSE. An endpoint PSE generates Ethernet dataand includes circuitry to provide power to powered device 16. On theother hand, a midspan PSE stands between a regular Ethernet switch andone or more PD subsystems 18, injecting power without affecting thetransmitted data.

In particular embodiments, power sourcing equipment 14 is responsiblefor determining the mode in which power will be delivered to powereddevice 16 and/or PD subsystems 18. For example, IEEE 802.3 describes twoavailable modes (called mode A and mode B) for transmitting power frompower sourcing equipment 14 to powered device 16. In mode A, pins 1 and2 may form one side of the supply voltage while pins 3 and 6 provide theother side (for the return voltage). In mode B, pins 4 and 5 may formone side of the supply voltage while pins 7 and 8 provide the other side(for the return voltage). In other modes, different and/or additionalpairs may be employed to provide a voltage source (through a supplyvoltage-return voltage combination). Moreover, in particularembodiments, different and/or additional pairs may be employed toprovide more than one voltage source. Each voltage source may be used topower an electrically-isolated PD subsystem 18.

Link 22 connects power sourcing equipment 14 to powered device 16 and PDsubsystems 18. In particular embodiments, link 22 is a standardtwisted-pair Ethernet cable. Link 22 may include four pairs. Inparticular embodiments, link 22 is used to connect two pairs to PDsubsystem 18 a and two other pairs to PD subsystem 18 b. In this manner,link 22 may allow each PD subsystem 18 a, 18 b to have a separatevoltage source along an electrically isolated power path. In certainembodiments, link 22 includes two or more standard Ethernet cables. Link22 may connect power sourcing equipment 14 and PD subsystems 18 in anysuitable way so as to allow the transmission of data while providingpower from power sourcing equipment 14 to powered device 16 and/or PDsubsystems 18.

Powered device 16 may be any device configured to receive power andexchange data with elements in system 10. For example, powered device 16may be an IP (internet protocol) phone, a web camera, a wireless accesspoint, an Ethernet hub, or any other device configured to receive powerthrough a standard twisted-pair Ethernet cable. In the illustratedembodiment, powered device 16 includes two PD subsystems 18 andinterface 20. While system 10 is shown including a single powered device16, it is to be understood that system 10 may include any suitablenumber of powered devices 16. For example, system 10 may include twopowered devices 16, each including one of PD subsystems 18 a, 18 b.

PD subsystems 18 are subsystems or devices powered by power sourcingequipment 14. Generally, each PD subsystem 18 contains circuitry toextract power. Each PD subsystem 18 may also exchange data with devicesin system 10. In particular embodiments, PD subsystem 18 and powereddevice 16 will be one and the same. In certain embodiments, as in theillustrated embodiment, powered device 16 will include multiple PDsubsystems 18. One or more of PD subsystems 18 may provide functionalityfor detecting the presence and/or availability of power sourcingequipment 14. In particular embodiments, PD subsystem(s) 18 providesIEEE detection ability.

By including multiple PD subsystems 18, powered device 16 mayelectrically isolate components within different PD subsystems 18.Isolating components allows electrical noise to be isolated. Forexample, powered device 16 may be a web camera that includes a cameramotor (which may be, for example, PD subsystem 18 a) and a physicalinterface including camera control circuitry (which may be, for example,PD subsystem 18 b). The camera motor circuits tend may be electricallynoisy, while camera control circuitry tends to require a power supplythat is electrically quiet. Because these circuits are in separate PDsubsystems 18 a, 18 b that are electrically isolated, electrical noisein one PD subsystem 18 may not be transferred to the other PD subsystem18. This may reduce the filtering that would be required if both PDsubsystems 18 a, 18 b shared a common supply rail.

As another example, powered device 16 may be an IP phone that benefitsfrom electrical isolation. The IP phone may include a physical interfaceincluding a central processing unit and digital signal processor (whichmay be, for example, PD subsystem 18 a) and an audio circuit for drivinga speaker (e.g., PD subsystem 18 b). Audio circuits may be sensitive toelectrical noise. By electrically isolating PD subsystems 18 a, 18 b,the amount of filtering required in the IP phone may be reduced.

Interface 20 allows communication and/or power transfer between PDsubsystems 18 while maintaining electrical isolation between those PDsubsystems 18. Interface 20 may have any of a variety of configurations.Example configurations of interface 20 that are designed to allowcommunication are provided with respect to FIGS. 3A, 3B, and 3C. Exampleconfigurations of interfaces that allow power transfer are provided withrespect to FIG. 2 (e.g., switch 38) and FIGS. 5A and 5B.

Particular embodiments of a system for facilitating communication andpower transfer between electrically-isolated PD subsystems 18 have beendescribed and are not intended to be all inclusive. While system 10 isdepicted as containing a certain configuration and arrangement ofelements, it should be noted that this is a logical depiction, and thecomponents and functionality of system 10 may be combined, separated anddistributed as appropriate both logically and physically. For example,while powered device 16 is illustrated as including two PD subsystems 18a, 18 b, it is to be understood that PD subsystems 18 a, 18 b may becomponents in any suitable device or devices. For example, system 10 mayfacilitate communication and power transfer between electricallyisolated PD subsystems 18 a, 18 b that are each contained in a separatepowered devices 16. Moreover, as illustrated, system 10 includes onlyone power sourcing equipment 14 connected to two PD subsystems 18;however, any suitable configuration and number of power sourcingequipment 14 and PD subsystems 18 may be employed in system 10. Thefunctionality described with respect to system 10 may be provided by anysuitable elements to facilitate communication and power transfer betweenelectrically-isolated PD subsystems.

FIG. 2 illustrates a powered device, indicated generally at 30, thatfacilitates communication between electrically-isolated powered device(PD) subsystems 34. In the illustrated embodiment, powered device 30includes a media dependent interface (MDI) 32, two PD subsystems 34 a,34 b, an interface 36, and a switch 38. In particular embodiments,powered device 30 is powered device 16 and PD subsystems 34 a, 34 b arePD subsystems 18 a, 18 b described above with respect to FIG. 1.

Powered device 30 receives power from power sourcing equipment (PSE) viaMDI 32. As illustrated, MDI 32 is shown in the common mode view andcontains four pairs 44 a, 44 b, 44 c, 44 d. Each pair 44 may be derivedfrom the center-tap of a transformer used to isolate the PHY from thecorresponding Ethernet MDI connections. In particular embodiments, pair44 a corresponds to pair (1,2) of a standard twisted-pair Ethernetcable; pair 44 b corresponds to pair (3,6) of a standard twisted-pairEthernet cable; pair 44 c corresponds to pair (4,5) of a standardtwisted-pair Ethernet cable; and pair 44 d corresponds to pair (7,8) ofa standard twisted-pair Ethernet cable. While MDI 32 is described andillustrated as including four pairs 44, it is to be understood that MDI32 may include any suitable number of pairs 44 or functionally similarcomponents.

In certain embodiments, two pairs 44 a, 44 b are employed to provide onepower path to PD subsystem 34 a, and two pairs 44 a, 44 b are employedto provide a second power path to PD subsystem 34 a. By using differentpairs to provide different power paths to each PD subsystem 34 a, 34 b,electrical isolation may be maintained. Moreover, by using two separatepower paths (each using two pairs 44), powered device 30 may effectivelydouble the available power received from power sourcing equipment 14.

As illustrated, powered device 30 includes two PD subsystems 34 a, 34 b.PD subsystem 34 a may be electrically isolated from PD subsystem 34 b,as is illustrated by isolation barrier 24. But, PD subsystem 34 a maycommunicate and transfer power to PD subsystem 34 b through interface36. Likewise, in particular embodiments, PD subsystem 34 b cancommunicate and transfer power to PD subsystem 34 a through interface36.

In the illustrated embodiment, each PD subsystem 34 includes acorresponding controller 40 and component 42. In particular embodiments,controller 40 may use the power received from power sourcing equipment14 to generate a supply voltage. In the illustrated embodiment, thesupply voltage generated by controller 40 a in PD subsystem 34 a islabeled V_(A), and the supply voltage generated by controller 40 b in PDsubsystem 34 b is labeled V_(B). These supply voltages are used by thecorresponding components 42 a, 42 b. Components 42 may be any deviceand/or circuitry in powered device 30. For example, when powered device30 is a web camera, components 42 a, 42 b may be a camera motor and aphysical interface including camera control circuitry. As anotherexample, when powered device 30 is an IP phone, components 42 a, 42 bmay be an audio circuit for driving a speaker and a physical interfaceincluding a central processing unit and digital signal processor.

Interface 36 allows communication and/or power transfer between PDsubsystems 34 while maintaining electrical isolation between those PDsubsystems 34. In particular embodiments, interface 36 is interface 20described above with respect to FIG. 1. Interface 36 may have any of avariety of configurations, and example configurations of interface 36are described with respect to FIGS. 3, 5A, and 5B.

Switch 38 may be included in powered device 30 in order to allow powereddevice 30 to transfer power between PD subsystems 34 a, 34 b. Inparticular embodiments, powered device 30 may include switch 38 in orderto facilitate interoperability with legacy systems. Powered device 30may close switch 38 to transfer power received on pairs 44 a, 44 b topairs 44 c, 44 d or vice versa. Similarly, if both PD subsystems 34 a,34 b obtain power from a PSE, then switch 38 may be opened. Inparticular embodiments, one of PD subsystems 34 a, 34 b opens switch 38after receiving a communication from the other PD subsystem 34. Thiscommunication may indicate that the other PD subsystem 34 has begunreceiving adequate power from the PSE. By closing switch 38, however,powered device may reduce or eliminate the electrical isolationpreviously maintained between PD subsystem 34 a and PD subsystem 34 b.Accordingly, in certain embodiments, switch 38 is included in powereddevice 30 and is employed only when powered device 30 requires that anunpowered one of PD subsystems 34 a, 34 b receive power. In certainembodiments, switch 38 is an electronic switch or a relay that ispowered and controlled by the initially powered PD subsystem 34. Switch38 may be employed to provide power to an indicator circuit that isoperable to report an underpowered condition. In certain embodiments,when closed, switch 38 connects V_(A) and V_(B). This may allow a PSE tovalidly detect an underpowered PD subsystem 34 even though it iscurrently receiving power through switch 38. In particular embodiments,powered device 30 does not include switch 38.

In operation, powered device 30 is powered by a PSE. The PSE may besubstantially similar to power sourcing equipment 14. Once it receivespower, powered device 30 may determine whether the PSE is delivering asufficient amount of power for the operation of powered device 30. Inorder to make this determination, PD subsystem 34 a and PD subsystem 34b may communicate. For example, PD subsystem 34 a may inform PDsubsystem 34 b of its power deficit. The power deficit may indicate theamount of power that PD subsystem 34 a requires in addition to the powerit is currently receiving from the PSE. Similarly, PD subsystem 34 b mayinform PD subsystem 34 a of its power deficit. If the total amount ofpower received by PD subsystem 34 a and PD subsystem 34 b is greaterthan or equal to the total amount of power required by both PDsubsystems 34 a, 34 b, then powered device 30 may determine that it isadequately powered.

Otherwise, powered device 30 may determine that an underpoweredcondition has occurred. In response, powered device 30 report theunderpowered condition. In particular embodiments, powered device 30 mayemploy circuitry in the powered PD subsystem 34 to report theunderpowered condition. For example, the powered one of PD subsystems 34may include a physical interface and control circuitry, which may beused to transmit a message indicating the underpowered status to the PSEor a control device in system 10. In certain embodiments, powered device30 may use an indicator circuit to report the underpowered condition. Anexample of such an indicator circuit is shown and described with respectto FIG. 4. While these two specific examples are described, it isunderstood that powered device 30 (or one or more of its components) mayuse any suitable methods to report an underpowered condition.

Also, when an underpowered condition occurs, powered device 30 may makethe best use of the power provided by the PSE. In particularembodiments, powered device 30 transfers power from the powered PDsubsystem 34 to the unpowered (or underpowered) PD subsystem 34. Incertain embodiments, powered device 30 may determine that power shouldbe transferred even though an underpowered condition did not occur. Forexample, one PD subsystem 34 may be underpowered while the other PDsubsystem 34 has sufficient power. In these situations, powered device30 may transfer power from the powered PD subsystem 34 to theunderpowered PD subsystem 34. Example circuits allowing such a powertransfer while maintaining electrical isolation are illustrated anddescribed in FIGS. 5A and 5B.

In general, PD subsystems 34 a, 34 b may communicate to cooperativelyaggregate their power needs, to request a sufficient total power fromthe PSE (while complying with standards limiting the power provided byeach power path), to control circuit operation within another PDsubsystem 34, and/or to accomplish other appropriate goals. Examplecircuits for allowing communications while maintaining electricalisolation are illustrated and described in FIG. 3. With bothcommunication and the ability to transfer power between PD subsystems34, two PD subsystems 34 may work together to negotiate the powerprovided by the PSE. The described decisions and determinations that areattributed to powered device 30 may be controlled by simple hardwarecircuitry or may be generated by a microprocessor implementing software.

Particular embodiments of a powered device 30 that facilitatescommunication between electrically-isolated powered devices have beendescribed and are not intended to be all inclusive. While powered device30 is depicted as containing a certain configuration and arrangement ofelements, it should be noted that this is a logical depiction, and thecomponents and functionality of powered device 30 may be combined,separated and distributed as appropriate both logically and physically.For example, while powered device 30 is depicted as including two PDsubsystems 34, it is to be understood that powered device 30 may includeany suitable number of PD subsystems 34. In certain embodiments, system10 includes at least two powered devices 30 each having one PD subsystem34, where the two PD subsystems 34 in the two powered devices 30 cancommunicate and transfer power through interface 36. As another example,MDI 32 may or may not be a component within powered device 30. And, as afinal example, while MDI 32 is depicted as containing four pairs 44, itis to be understood that MDI 32 may contain any suitable components toprovide any number of distinct power paths to powered device 30.

FIG. 3 illustrates three example interfaces that maintain electricalisolation while allowing communications to be sent through theinterface. As illustrated, FIG. 3 shows a capacitively coupled interface50, a transformer coupled interface 52, and an opto-coupler interface54. In particular embodiments, interface 36 (described above withrespect to FIG. 2) is capacitively coupled interface 50, transformercoupled interface 52, or an opto-coupler interface 54.

In particular embodiments, capacitively coupled interface 50 is used inorder to allow communications while preserving electrical isolation. Forexample, capacitively coupled interface 50 may allow communicationsbetween electrically-isolated PD subsystems 18, 34. Capacitively coupledinterface 50 may preserve electrical isolation by reducing oreliminating the amount of direct current (DC) that is able to flowbetween isolated sections. As illustrated, capacitively coupledinterface 50 includes two capacitors 56 a, 56 b in series and oneadditional capacitor 56 c connecting the two series capacitors acrossV_(OUT). In operation, capacitively coupled interface 50 receives asignal encoded in a time varying current. This signal is received at V.Because the signal has an alternating voltage, the signal may beminimally filtered as it passes through capacitors 56 a, 56 b, 56 c.Accordingly, capacitively coupled interface 50 may send a signal fromV_(IN) to V_(OUT) while preserving electrical isolation. Capacitivelycoupled interface 50 may relay signals transmitted in either direction.

In certain embodiments, transformer coupled interface 52 is used inorder to allow communications while preserving electrical isolation. Forexample, transformer coupled interface 52 may allow communicationsbetween electrically-isolated PD subsystems 18, 34. Transformer coupledinterface 52 may preserve electrical isolation by reducing oreliminating the amount of DC current that is able to flow betweenisolated sections. As illustrated, transformer coupled interface 52includes an isolation transformer with an N:1 ratio. One side of thetransformer connects to V_(IN), while the other side connects toV_(ouT). A transformer electrically isolates direct current (DC), butmay relay a signal's time varying current components. Accordingly,transformer coupled interface 52 may permit communication whilepreserving electrical isolation. Transformer coupled interface 52 mayrelay signals transmitted in either direction.

In some embodiments, opto-coupler interface 54 is used in order to allowcommunications while preserving electrical isolation. For example,opto-coupler interface 54 may allow communications betweenelectrically-isolated PD subsystems 18, 34. Opto-coupler interface 54may preserve electrical isolation by reducing or eliminating the amountof direct current (DC) that is able to flow from V_(IN) to V_(OUT).Among other elements, the illustrated opto-coupler interface 54 includesa light emitting diode (LED) 58 and a light sensitive transistor 60. Inthe illustrated embodiment of opto-coupler interface 54, data isreceived by V_(IN), causing the voltage on the output of amplifier 62 tobe greater than the reference voltage. Current will flow through LED 58,causing LED 58 to generate light. This light is sensed by transistor 60,which draws current from high voltage (V_(S)). The presence or absenceof this current flow directly affects the output of amplifier 64—namely,V_(OUT). By this process, opto-coupler interface 54 may send thereceived signal to V_(OUT) while preserving electrical isolation. In theillustrated embodiment, opto-coupler interface 54 is only able to relaysignals transmitted in one direction (from V_(IN) to V_(OUT)). However,it is to be understood that a similar circuitry may be incorporated toallow communication in the opposite direction. In particularembodiments, opto-coupler interface 54 may receive differential inputsso that LED 58 is driven when a positive input is detected and it is notdriven when a negative input is detected, for example. Whileopto-coupler interface 54 is illustrated as including connections toreference or ground voltages, it is to be understood that any suitablevoltages may be used in place of these connections.

Particular embodiments of a network device interface have been describedand are not intended to be all inclusive. While capacitively coupledinterface 50, transformer coupled interface 52, and opto-couplerinterface 54 are each depicted as containing a certain configuration andarrangement of elements, it should be noted that these are simplyexamples. The elements within these interfaces 50, 52, 54 may becombined, separated and distributed as appropriate. A powered deviceand/or PD subsystem(s) may employ any suitable interface(s) thatmaintains electrical isolation while allowing communication through theinterface.

FIG. 4 is an example circuit, indicated generally at 80, for reportingthat a PD subsystem 34 is underpowered. As explained briefly above,powered device 30 can provide a notification that it is underpowered.The underpowered condition may occur when powered device 30 is connectedto legacy power sourcing equipment. In the illustrated embodiment,circuit 80 is designed to report when PD subsystem 34 a is underpowered.A similar circuit can also be included to report when PD subsystem 34 b,powered device 30, or other powered devices or PD subsystems areunderpowered.

Circuit 80 is connected to V_(S-A), V_(S-B), and ground. As illustrated,V_(S-A) is the supply voltage for PD subsystem 34 a and may be derivedfrom V_(A) (the voltage supplied to component 42 a within PD subsystem34 a). As illustrated, V_(S-B) is the supply voltage for PD subsystem 34b and may be derived from V_(B) (the voltage supplied to component 42 bwithin PD subsystem 34 b). While circuit 80 is illustrated as havingthese example connections, it is to be understood that any suitablevoltages may be connected to circuit 80. For example, portions ofcircuit 80 illustrated as connecting to a common ground may connect toany suitable reference voltage(s).

In the illustrated embodiment, circuit 80 includes two light emittingdiodes (LEDs) 82, 84, a light sensitive transistor 86, a standardtransistor 88, and two resistors 82, 84. When PD subsystem 34 b ispowered and PD subsystem 34 a is not powered (or underpowered), V_(S-A)will be approximately equal to 0 V and V_(S-B) will have a voltage (inother words, will be sufficiently greater than 0 V). With V_(S-A) notpresent, LED 82 will not be illuminated. This will cause transistor 86to not be driven, resulting in a high voltage at the base of transistor88. (Transistor 88 may be a bipolar transistor, a MOSFET transistor, orany other appropriate component.) This high base will drive transistor88, causing current to flow through LED 84. Accordingly, LED 84 may beilluminated when PD subsystem 18 a is underpowered.

Particular embodiments of a circuit for reporting that a component inthe network device is underpowered have been described and are notintended to be all inclusive. While circuit 80 is depicted as containinga certain configuration and arrangement of elements, it should be notedthat this is simply an example. The elements within this circuit may becombined, separated and distributed as appropriate. Different circuitscontaining some, all, or none of the elements described in circuit 80may be used to report that a component in a powered device isunderpowered.

FIGS. 5A-5B illustrate example circuits for transferring power betweenelectrically-isolated PD subsystems. FIG. 5A illustrates a circuit 100for transferring power from a first PD subsystem 34 a to a second PDsubsystem 34 b. Within the following explained example, assume that PDsubsystem 34 a is powered while PD subsystem 34 b is not powered. V_(IN)may be connected to the supply voltage of the powered PD subsystem 34 a(in this example, V_(S-A)), and V_(OUT) may be connected to the supplyvoltage of the unpowered PD subsystem 34 b (in this example, V_(S-B)).

As illustrated, circuit 100 includes three capacitors 102 a, 102 b, 102c and a switch 104. In an example operation, switch 104 may be openedand closed at a particular frequency in order to transfer power from thepowered PD subsystem 18 to the unpowered PD subsystem (in this example,from PD subsystem 34 a to PD subsystem 34 b). In an example operation,switch 104 may be opened and closed at a rate of “f” with a nominal 50%duty cycle. The values of the capacitors 102 a, 102 b, 102 c and theduty cycle selected will alter the available output current (I_(OUT))and average output voltage (V_(OUT)). In the illustrated embodiment, therelation between I_(OUT), V_(OUT), V_(IN), f, and the values of thecapacitors 102 a, 102 b, and 102 c (C₁, C₂, and C₃, respectively) isgiven by the following equation:

I_(OUT) ≤ −C₃(V_(IN) − V_(OUT))f$V_{OUT} \leq {{V_{IN}\left( \frac{C_{1}C_{2}}{C_{1} + C_{2}} \right)}/\left( {\frac{C_{1}C_{2}}{C_{1} + C_{2}} + C_{3}} \right)}$

In particular embodiments, circuit 100 further includes filter and/orvoltage regulation circuits. In certain embodiments, a diode is used inplace of or in addition to switch 104. This diode may be designed toconduct when V_(IN) is present (e.g., greater than 0 V) and preventconduction when V_(IN) is absent (e.g., approximately equal to 0 V).

In certain embodiments, circuit 100 provides less power to PD subsystem34 b than PD subsystem 34 b would be able to obtain directly whenpowered by power sourcing equipment 14. However, circuit 100 may enableminimal circuit function to be accomplished in PD subsystem 34 b when itwould otherwise remain unpowered. For example, powered device 30 may bean IP phone and PD subsystem 34 b may be the IP phone's audiosubsection, which drives a handset and a speaker phone. If PD subsystem34 b obtains power directly from power sourcing equipment 14, then PDsubsystem 34 b may have enough power to use the handset and/or thespeaker phone. However, if circuit 100 transfers power from PD subsystem34 a to PD subsystem 34 b, PD subsystem 34 b may have only enough powerto operate an IP phone's handset.

While circuit 100 has been described as transferring power from PDsubsystem 34 a to PD subsystem 34 b, it is to be understood that theseprinciples are equally applicable for a power transfer from PD subsystem34 b to PD subsystem 34 a. In that situation, V_(IN) may be connected tothe supply voltage of PD subsystem 34 b (V_(S-B)), and V_(OUT) may beconnected to the supply voltage of PD subsystem 34 a (V_(S-A)).

FIG. 5B illustrates another example circuit 110 for transferring powerbetween PD subsystems 34. As illustrated, circuit 110 connects to V_(A),V_(S-A), V_(B), V_(S-B), and ground. V_(A) and V_(B) may be voltagescorresponding to the power received from power sourcing equipment 14,and V_(S-A) and V_(S-B) may be the supply voltages used by components 42a, 42 b within PD subsystems 34 a, 34 b, respectively. In an exampleembodiment, circuit 110 is employed in powered device 16, where powereddevice 16 is a web camera that includes two PD subsystems 34 a, 34 b. PDsubsystem 34 a may include the central processing unit and signalprocessing circuitry, and PD subsystem 34 b may include the tilt, pan,and zoom motors. For this embodiment, V_(S-A) may be the supply voltageused to power the central processing unit and signal processingcircuitry, while V_(S-B) may be the supply voltage used to power thecamera's motors. While circuit 110 is illustrated as having theseexample connections, it is to be understood that any suitable voltagesmay be connected to circuit 110. For example, portions of circuit 110illustrated as connecting to a common ground may connect to differentgrounded voltages.

Circuit 110 includes a flyback DC-to-DC design. In the illustratedembodiment, circuit 110 includes switches 112, 114, 116, synchronousrectifiers 118, 120, transformer 122 including inductors 124 a, 124 b,124 c, and transformer 126 including inductors 128 a, 128 b, 128 c.Switches 112, 114 may control the amount of power drawn from power madeavailable by power sourcing equipment. Switch 116 may control the amountof power transferred between PD subsystems 34 a, 34 b. Synchronousrectifier 118 and transformer 122 (and its inductors 124 a, 124 b, 124c) may work with other circuit elements to transfer power from V_(A) (orsubcircuit 134 b) to the supply voltage V_(S-A). Likewise, synchronousrectifier 120 and transformer 126 (and its inductors 128 a, 128 b, 128c) may work with other circuit elements to transfer power from V_(B) (orsubcircuit 134 a) to the supply voltage V_(S-B).

In an example situation, both PD subsystems 34 a, 34 b are powered. Inparticular embodiments, no power is transferred between PD subsystems 34a, 34 b when both PD subsystems are powered. In this case, switch 116remains open and subcircuits 134 a, 134 b each operate independently. Insubcircuit 134 a, for example, switch 112 may be closed sequentially inorder to build up energy in inductors 124 a, 124 b. This energy may beextracted from V_(A). Synchronous rectifier 118 may then operate totransfer energy from inductor 124 to V_(S-A). In particular embodiments,subcircuit 134 a and its constituent elements are controlled by PDsubsystem 34 a. In a similar manner, subcircuit 134 b may uses switch114, inductors 128 a, 128 b, and synchronous rectifier 120 to transferenergy from V_(B) to V_(S-B). Subcircuit 134 b and its constituentelements may be controlled by PD subsystem 34 b.

In a second example situation, only one of PD subsystems 34 a, 34 b ispowered. When only one of PD subsystems 34 is powered (and the other isnot powered), switch 116 can be controlled to transfer energy from thepowered PD subsystem 34 to the unpowered PD subsystem 34. For thepurposes of this example, assume that PD subsystem 34 a is powered whilePD subsystem 34 b is not powered. In this example, V_(A) has a voltage(e.g., V_(A)>0 V), but V_(B) does not have a voltage (e.g., V_(B)˜0 V).

Switch 116 may control the amount of power transferred between PDsubsystems 34 (in this case, from PD subsystem 34 a to PD subsystem 34b). In particular embodiments, switch 116 is opened and closed at a rateof “f,” with a nominal 50% duty cycle. The duty cycle selected may alterthe amount of current and voltage that is transferred. The length oftime that switch 116 is closed may determine the amount of powertransferred from PD subsystem 34 a to PD subsystem 34 b. By opening andclosing switch 116, energy is transferred from transformer 122 totransformer 126 by way of inductors 124 c, 128 c. Transformer 126 maythen transfer energy to inductors 128 a, 128 b. As explained above,subcircuit 134 b can be controlled so that energy can be transferredfrom transformer 126 (and its inductors 128 a, 128 b) to V_(S-B).

In an example operation for transferring power in this second situation,switch 112 is closed first to transfer energy from V_(A) to transformer122. Then, switch 116 is closed to transfer energy from transformer 122to transformer 126. After the energy has transferred, both switch 112and switch 116 may be opened. At the same time, synchronous rectifiers118, 120 may be turned on in order to transfer energy from transformers122, 126 to V_(S-A) and V_(S-B), respectively. This example operationmay then repeat to continue the flow of power.

In a third example situation, both PD subsystems 34 a, 34 b are powered,and circuit 110 is employed to transfer power between PD subsystems 34a, 34 b. This third example operation may employ a similar operation aswas described with respect to the second example operation. For example,switch 112 may be closed to transfer energy from V_(A) to transformer122, and switch 114 may be closed to transfer energy from V_(B) totransformer 126. Then, switch 114 may be opened while switch 116 isclosed to transfer energy from transformer 122 to transformer 126. Afterthe energy has transferred, switches 112, 116 may be opened. At the sametime, synchronous rectifiers 118, 120 may be turned on in order totransfer energy from transformers 122, 126 to V_(S-A) and V_(S-B),respectively. This example operation may then repeat to continue theflow of power.

Using circuit 110, power transfer may be accomplished while keeping thepower supply voltages (e.g., V_(S-A) and V_(S-B)) in each PD subsystem34 a, 34 b electrically-isolated from each other. In certainembodiments, the powered PD subsystem 34 controls switch 116 fromstartup (e.g., when V_(S-A)≈V_(S-B)≈0) until the supply voltage of theunpowered PD subsystem 34 (e.g., V_(S-A) or V_(S-B)) reaches apredetermined level. Once the supply voltage of the unpowered PDsubsystem 34 has reached a particular level, control of switch 116 maypass to the unpowered PD subsystem 34. In particular embodiments, switch116 is only closed when both switch 112 and switch 114 are also closed.Moreover, in the illustrated embodiment, circuit 110 is simplified tohighlight the inductive coupling mechanism. In other embodiments,circuit 110 may include any suitable additional and/or alternatecomponents.

Particular embodiments of a circuit for transferring power betweenelectrically-isolated powered devices have been described and are notintended to be all inclusive. While circuit 100 and circuit 110 aredepicted as containing a certain configuration and arrangement ofelements, it should be noted that this is simply an example. Theelements within this circuit may be combined, separated and distributedas appropriate. For example, circuit 110 may or may not includeinductors 124 b, 128 b. In particular embodiments, circuit 110 includesonly one of inductors 124 b, 128 b so that all received power may betransferred to a common supply voltage (V_(S-A) or V_(S-B)). As anotherexample, circuit 110 may contain a single transformer 122, 126. Incertain embodiments, circuit 110 combines transformers 122, 126,eliminates inductors 124 c, 128 c, and operates switches 112, 114 out ofphase in order to transfer power to the respective supply voltages. As athird example, circuit 110 may combine the supply voltages (V_(S-A) orV_(S-B)) in any suitable manner as is known to those of skill in theart.

Different circuits containing some, all, or none of the elementsdescribed in circuits 100, 110 may be used to transfer power betweenelectrically-isolated PD subsystems. In particular embodiments, ratherthan employing circuit 100 or circuit 110, powered device 30 includesswitch 38 in order to transfer power between different PD subsystems 34.

FIG. 6 is a flowchart illustrating a method, indicated generally at 150,for obtaining power and reporting an underpowered condition utilizingcommunication and power transfer between electrically-isolated PDsubsystems.

At step 152, one or more of PD subsystems 34 a, 34 b receives power frompower sourcing equipment 14. At step 154, PD subsystems 34 a, 34 bcommunicate regarding the amount of power received from power sourcingequipment 14. This communication may also provide an indication of apower deficit. The power deficit may represent the amount of power thata particular PD subsystem 34 needs in addition to the power actuallyreceived by power sourcing equipment 14. In particular embodiments, thepower deficit indicates when a particular PD subsystem 34 has receivedpower in excess of its needs. After PD subsystems 34 a, 34 b communicateregarding the power received, PD subsystem 34 a may determine whetherthe total power received by both PD subsystems 34 is sufficient, in step156. If the power is sufficient, method 150 proceeds to step 166.

Otherwise, at step 158, PD subsystem 34 a determines whether or not toreport an underpowered condition. If PD subsystem 34 a decides to reportan underpowered condition, then an indication of the underpowered statusis provided in step 160. In particular embodiment, a circuit containinga light emitting diode (LED) causes the LED to be illuminated in orderto provide the indication of the underpowered status. In certainembodiments, powered circuitry within PD subsystem 34 a generates andtransmits a message to power sourcing equipment 14 or another device insystem 10. This message may provide the indication of and informationregarding the underpowered status.

At step 162, PD subsystem 34 a determines whether power needs to betransferred between PD subsystem 34 a and PD subsystem 34 b. If power isto be transferred, PD subsystem 34 a initiates the power transfer atstep 164. In particular embodiments, PD subsystem 34 a transfers powerto PD subsystem 34 b using a flyback DC-to-DC circuit. An example of asuitable flyback DC-to-DC circuit is shown and described with respect toFIG. 5B. Once power transfer is complete, method 150 ends.

At step 166, PD subsystem 34 a determines whether each of PD subsystems34 a, 34 b has sufficient power. In particular embodiments, PD subsystem34 b will not have sufficient power even though the aggregate amount ofpower received by both PD subsystem 34 a and PD subsystem 34 b issufficient for their combined needs. If PD subsystem 34 a determinesthat one of PD subsystems 34 a does not have sufficient power, thenmethod 150 returns to step 164, where power transfer is initiatedbetween PD subsystems 34 a, 34 b. Otherwise, method 150 ends.

The method described with respect to FIG. 6 is merely illustrative, andit is understood that the manner of operation and devices indicated asperforming the operations may be modified in any appropriate manner.While the method describes particular steps performed in a specificorder, it should be understood that system 10 contemplates any suitablecollection and arrangement of elements performing some, all, or none ofthese steps in any operable order. For example, while PD subsystem 34 ais described as performing various steps, any suitable components mayperform these steps, including powered device 30 and/or PD subsystem 34b. Moreover, the described decisions and determinations may becontrolled by simple hardware circuitry or may be generated by amicroprocessor implementing software.

Although the present invention has been described in severalembodiments, a myriad of changes and modifications may be suggested toone skilled in the art, and it is intended that the present inventionencompass such changes and modifications as fall within the presentappended claims.

1-20. (canceled)
 21. A system comprising: a powered device comprising: afirst powered device (PD) subsystem; a second powered device (PD)subsystem electrically isolated from the first PD subsystem; aninterface connecting the first PD subsystem and the second PD subsystemwherein the first PD subsystem is operable to receive a communicationfrom the second PD subsystem through the interface; and power sourcingequipment (PSE) connected to the powered device by a link and operableto provide power to both the first PD subsystem and the second PDsubsystem through the link.
 22. The system of claim 21 wherein the firstPD subsystem is further operable to transfer power to the second PDsubsystem through the interface.
 23. The system of claim 21 wherein theinterface comprises one or more of the following circuits: acapacitively coupled interface, a transformer coupled interface, anopto-coupler interface, and a flyback DC-to-DC circuit.
 24. The systemof claim 21 wherein the second PD subsystem is operable to receive acommunication from the first PD subsystem through the interface and totransfer power to the first PD subsystem through the interface.
 25. Thesystem of claim 21 wherein: the link comprises a standard twisted-pairEthernet cable including four pairs; the PSE is operable to providepower to the first PD subsystem through a first pair and a second pairof the link; and the PSE is further operable to provide power to thesecond PD subsystem through a third pair and a fourth pair of the link.26. The system of claim 21 wherein the first PD subsystem and the secondPD subsystem communicate in order to: determine a total power levelrepresenting power requirements of both the first PD subsystem and thesecond PD subsystem; and compare the total power level to a receivedpower level, the received power level representing power received fromthe PSE by both the first PD subsystem and the second PD subsystem. 27.The system of claim 26 wherein an indicator circuit is operable toprovide an indication that the powered device is underpowered when thereceived power level is less than the total power level.
 28. The systemof claim 21 wherein the first PD subsystem is operable to transfer powerto the second PD subsystem when the communication indicates that thesecond PD subsystem is underpowered.
 29. The system of claim 21 whereinthe first PD subsystem is operable to transfer power through theinterface to the second PD subsystem using a flyback DC-to-DC circuit.30. A method comprising: receiving a first amount of power at a firstpowered device (PD) subsystem from power sourcing equipment (PSE), thefirst amount of power received on a link connecting the PSE to a powereddevice, the powered device comprising the first PD subsystem and asecond powered device (PD) subsystem, the second PD subsystemelectrically isolated from the first PD subsystem and powered by the PSEover the link connecting the PSE to the powered device; receiving anidentification of a second amount of power from the second PD subsystem,the second amount of power representing a power deficit of the second PDsubsystem; based on the first amount of power and the second amount ofpower, determining whether to transfer power from the first PD subsystemto the second PD subsystem; maintaining electrical isolation between thefirst PD subsystem and the second PD subsystem when power is transferredfrom the first PD subsystem to the second PD subsystem.
 31. The methodof claim 30 wherein: an interface connects the first PD subsystem andthe second PD subsystem; and the first PD subsystem is operable toreceive a communication from the second PD subsystem through theinterface and to transfer power to the second PD subsystem through theinterface.
 32. The method of claim 31 wherein the interface comprisesone or more of the following circuits: a capacitively coupled interface,a transformer coupled interface, an opto-coupler interface, and aflyback DC-to-DC circuit.
 33. The method of claim 30 wherein: the linkcomprises a standard twisted-pair Ethernet cable including four pairs;the PSE is operable to provide power to the first PD subsystem through afirst pair and a second pair of the link; and the PSE is furtheroperable to provide power to the second PD subsystem through a thirdpair and a fourth pair of the link.
 34. The method of claim 30 furthercomprising: determining a total power level representing powerrequirements of both the first PD subsystem and the second PD subsystem;and comparing the total power level to a received power level, thereceived power level representing power received from the PSE by boththe first PD subsystem and the second PD subsystem.
 35. The method ofclaim 34 wherein an indicator circuit is operable to provide anindication that the powered device is underpowered when the receivedpower level is less than the total power level.
 36. The method of claim30 wherein the identification of the second amount of power indicatesone of the following: that the second PD subsystem has sufficient power,and a power requirement of the second PD subsystem.
 37. The method ofclaim 30 wherein the determination of whether to transfer powercomprises: identifying a third amount of power, the third amount ofpower representing a power requirement of the first PD subsystem; if thefirst amount of power is greater than the sum of the second amount ofpower and the third amount of power, then transferring power from thefirst PD subsystem to the second PD subsystem.
 38. The method of claim30 wherein the first PD subsystem is operable to transfer power to thesecond PD subsystem using a flyback DC-to-DC circuit.
 39. An apparatuscomprising: a first powered device (PD) subsystem operable to receive afirst amount of power from power sourcing equipment (PSE), the firstamount of power received on a link connecting the PSE to the first PDsubsystem; a second powered device (PD) subsystem electrically isolatedfrom the first PD subsystem, the second PD subsystem operable receive asecond amount of power from the PSE on the link, the link furtherconnecting the PSE to the second PD subsystem; and an interfaceconnecting the first PD subsystem and the second PD subsystem whereinthe first PD subsystem is operable to receive a communication from thesecond PD subsystem through the interface and to transfer power to thesecond PD subsystem through the interface.
 40. The apparatus of claim 39wherein: the link comprises a standard twisted-pair Ethernet cableincluding four pairs; the PSE is connected to the first PD subsystemthrough a first pair and a second pair of the link; and the PSE isconnected to the second PD subsystem through a third pair and a fourthpair of the link.